The present invention relates to a plasma processing method using a plasma processing apparatus. More particularly, it relates to a plasma cleaning in the plasma processing method.
In order to enhance the productivity of semiconductor devices in the semiconductor processing field, it is requested that, in the plasma etching, the dropping of microscopic particles onto a microminiaturized structure fabricated on a wafer is reduced to the minimum possible degree. The mechanisms of the emission of the particles are explained as follows. Deposition film formed during wafer processing on the inner-wall surface of a processing chamber and on parts inside the chamber is re-injected onto the wafer. Or the material itself constituting the surface of the inner-wall and the parts is emitted and dropped onto the surface of the wafer. In view of this situation, as measures for reducing the emission of the microscopic particles, the following method or configuration is devised and used. Namely, a plasma cleaning method for removing the deposited film can be used. Otherwise, a material which can prevent the emission of the microscopic particles is used as the inner-wall surface and the inside parts of a processing chamber.
As the conventional technology for reducing the emission of the microscopic particles, there exists the method of applying the plasma cleaning to the deposited film after the wafer processing. In JP-A-10-261623, the emission of the microscopic particles is reduced as follows. Namely, in addition to the conventional plasma-cleaning-based method of removing deposited films, the emission of the microscopic particles is reduced by using a plasma which is capable of chemically decomposing and removing a chemical compound formed between the inner-wall material released into the processing chamber and a processing gas used. Also, in JP-A-10-233388, the emission of the microscopic particles is reduced as follows. Namely, after the deposited-film removing step is over, the emission of the microscopic particles is reduced by adding a step that releases the reaction product of residual adsorbed gases from the inner-wall surface into the processing chamber. Here, this releasing operation is performed by exposing the inner-wall surface to plasma for a short time of a few hundreds of milliseconds to a few seconds.
In mass production of the devices, the amount of deposit material or the chemical compound which is formed from the processing chamber's inner-wall material and the processing gas is increased with increasing the time of the continuous processing of wafers. As a result, the number of the microscopic particles is increased. In order to address this problem, the apparatus is disassembled, and the washing or replacing operation for the processing chamber's inner-wall parts is carried out. In order to restart wafer processing after these operations, however, the start-up of the processing chamber takes a few hours to about a day. In addition, the start up time decreases the productivity of the devices. Accordingly, it is requested to provide a plasma processing apparatus or plasma-processing operating method which makes it possible to continue the plasma processing over a longer time in a state where the number of the microscopic particles is small.
On the surface of the wafer, there exist an area where the microminiaturized structure is fabricated with high density and an area of that with low density. When the microscopic particles drop onto the area of the low density of the structure, the dropped microscopic particles exert only a little influence on a decrease in the yield of the device. This situation holds as long as the microscopic particles are sufficiently smaller as compared with the structure. Meanwhile, when the microscopic particles drop onto the area of the high density of the structure, it becomes highly possible that the yield decreases with the worsening of the etching profile under the dropped particles. Also, the worsened area is enlarged in proportion to the size of the particles and the yield decreases. Consequently, with the development of microminiaturization in a semiconductor processing in recent years, it is requested that the number of the microscopic particles which will drop onto a wafer and the diameter of the particles are decreased as small as possible.
As described above, one of the causes for the emission of the microscopic particles is as follows. Namely, the processing chamber's inner-wall material is sputtered by the plasma used. Then, the sputtered inner-wall material is released into the processing chamber as the microscopic particles. Accordingly, it is preferable that a material which has tremendously high resistance to the plasma sputtering is employed as the processing chamber's inner-wall material. In view of this situation, in recent years, there has been more employment of the following new plasma-resistant materials: a sprayed-on product or sintered body of yttria (which, hereinafter, will be referred to as “Y2O3”), and Y2O3 or alumina (Al2O3) to which a trace amount of various elements such as zirconia is added for the purpose of enhancing the plasma-resistant property.